The role of ethylene in plant biology has been the subject of numerous studies for over 50 years (see Ethylene in Plant Biology by F. B. Abeles, Academic Press, 1973). While in certain cases, the effects of ethylene are highly desirable at certain stages of plant development, it is also beneficial in other stages to inhibit and/or in some way monitor the extent of such effects in plant development.
Since ethylene is a naturally occurring hormone in plants, its hormonal influence is always present. However, ethylene effects are often magnified beyond desirable limits by stress situations such as trauma caused by application of chemicals, insect damage, temperature extremes, drought, .gamma.-irradiation, disease, mechanical wounding, unfavorable biological environment or other phenomena which stimulate the plant's natural metabolism to form an increased supply of this hormone. Generally, older plant tissue has less tolerance for contact with foreign chemicals than young tissue so that a phytotoxic affect, evidenced by increased ethylene production, is more easily induced. Young tissue, which is less specialized exhibits significantly higher dosage tolerances before triggering the plant's defence mechanism to counteract the influence of foreign chemicals.
Some of the deleterious effects on plants caused by ethylene imbalance include premature breaking of seed, bud, tuber, corm or bulb dormancy; the stimulation of fungal spore germination and increased growth rate of molds; leaf abnormalities and hypertrophy of cortex tissue; spoilage of picked fruit; abortion of fruit and flower buds; unseasonal ripening of fruits; leaf senescence; the reduction of protein levels and immature development of fruit; rapid defoliation which results in plant morphology; and many more which are extensively described in numerous publications and texts. The above are only a few of the undesirable effects resulting from an inordinate supply of ethylene in the plant.
Departure from the normal levels of hormones and proteins in plant cells, such as may be experienced due to stress, induced, e.g., by a disease or injury situation, can result in secondary changes which deleteriously affect growth and development of the cell and plant. Many of the abnormal developments widely discussed, particularly epinasty and tissue proliferation, are due to such secondary effects caused by such imbalance of the ethylene hormone in plant tissue.
In addition to avoiding the disadvantages caused by stress ethylene production, it is also desirable in certain situations to depress normal ethylene formation in a plant, e.g. to delay normal senescence, defoliation, sprouting, ripening, spoilage of picked fruit or vegetables and to extend the period for crop development before ripening so as to promote a larger, more fully developed produce. Accordingly, it is the aim of present research to provide a method, a chemical or a composition which is capable of closely controlling, blocking and/or monitoring ethylene production in plants to prevent untimely metabolic effects and to generally provide healthy development in the plant while promoting certain desired effects for improved harvesting and yield of high quality crops.
It is an object of the present invention to provide such a compound, capable of closely regulating and altering the rate of in vivo ethylene production and varying plant response wherever applied to meet specific needs.
Another object of the present invention is to provide a process for applying a compound which is biologically non-phytotoxic to plant life.
Still another object of this invention is to utilize a readily available and economical compound for the control of biological effects caused by a plant hormone.
Still another object is to provide a process for significantly preserving the freshness of cut flowers.
Still another object is to provide a treatment which inhibits in vivo generation of ethylene, causing spoilage of picked fruit.
Another object is to regulate ripening of growing crops to obtain maximum size and development and to coincide with the most advantageous season for harvesting so as to avoid damage due to frost or rain and to avoid second and third seasonal harvesting.
These and other objects of the invention will become apparent from the accompanying description and disclosure.
According to this invention, there is provided an agent for inhibiting in vivo ethylene production in plants, said agent being a monaza amine and/or amide represented by the formula: ##STR1## wherein each X is CH or CH.sub.2 ; n is an integer having a value of 3 or 4; Y is CH, CH.sub.2 or C.dbd.O and Z is hydrogen or alkyl of 1 to 3 carbon atoms which is optionally substituted with a hydroxy group. Of these compounds, those having at least one doubly bonded carbon atom wherein Z is hydrogen or alkyl of 1 to 2 carbon atoms are preferred, and N-methyl-2-pyrrolidone is most preferred.
Representative of the preferred ethylene inhibiting agents of the present invention are N-methyl-2-piperidone, N-(ethyl)-2-pyrrolidone, N-(hydroxyethyl)-2-pyrrolidone, N-ethyl-2-piperidone, 2-pyrrolidone, N-methyl-2-pyrrolidone, N-(hydroxymethyl)-2-pyrrolidone, N-methylpyrrole, N-methylhydroxypiperidone, N-methyl-2-pyridone, N-(ethyl)-2-pyridone, trihydro-N-methyl pyridine, N-methyl-hydropyridine, 2-piperidone, 2-pyridone, N-methylpyrroline, 2-pyrrolone, N-methyl-2-pyrrolone, etc. N-methyl-2-pyrrolidone is the most effective of these chemical agents and is additionally preferred because of its availability, its chemical properties, such as low vapor pressure and freezing point which provide stability over a wide range of climatic conditions, its non-phytotoxic nature and solubility in a wide variety of chemicals which allows for its incorporation in various agricultural formulations, e.g. in combination with a liquid solvent or in more complex compositions additionally including a fungicide, herbicide, nematocide, and/or another active agricultural plant growth regulating chemicals.
Ethylene inhibiting agents such as N-(isopropyl)-2-pyrrolidone, N-methylpiperidine, N-methylpyrrolidine, N-ethylpyrrolidine, e.g. those inhibiting agents which contain no doubly bonded carbon atom or have propyl substituent on the nitrogen, appear to have somewhat limited effect and are recommended only for plants which have not achieved full maturity or young tissue. On mature plants these agents induce a phytotoxic response at acceptable dosage levels so that their use in such cases is not recommended.
Although the heterocyclic compounds of the present invention may be applied directly to the plant, for economic reasons and for better coverage and distribution, the present agents are usually employed in a composition, e.g. mixed with an inert diluent or carrier which is preferably a liquid such as water, xylene, toluene, cyclohexane or other paraffins, a mineral oil fraction, a vegetable oil, or any other conventional and inert organic liquid, or mixtures thereof which are commonly employed as inert extenders in agricultural applications.
For the purposes of the present invention, the concentration of the present inhibiting agent in a composition applied to a plant is within the range of between about 150 ppm and about 5,000 ppm, preferably between about 500 ppm and about 3,500 ppm and most preferably an amount not in excess of about 3,000 ppm. Generally, the inhibiting affect of the present agents is more pronounced in seedlings, usually considered to include plants through the third foliate stage, and least effective in fully developed plants whose vegetative growth increase has substantially ceased. However, since the stress tolerance of older plant tissue varies somewhat with the species of ethylene inhibitor applied, it is recommended that the more active species of the present agents or those which tend to have an irritating influence at certain stages of plant development, be emloyed in a concentration within a lower portion of the above range, so as to avoid a stress situation capable of inducing a phytotoxic influence by temporarily increasing the generation of ethylene. Of the present agents, N-methyl-2-pyrrlidone exerts a consistent inhibitory effect at all concentration levels tested. Those agents which are not preferred perform best at higher dosage levels, e.g., about 2,000 ppm to about 5,000 ppm depending on the age of the plant and the agent selected.
The inhibiting agent is conveniently employed in a composition with an extender. The liquid carrier or extender may optionally contain a convention amount of surface active agent such as a polyoxyalkylene fatty acid ester or alcohol, ether, lignin, methyl cellulose, etc.; although such is not needed to provide the foregoing benefits of this invention. Also, water diluent can be employed with an auxiliary organic solvent which may be selected from those listed above. Thickeners and emulsifiers such as guar gum, locust bean gum, palm oil or latexes and vegetable oils can also be added to prevent removal by rain or other chemical sprays.
It is to be understood, however, that the present N-heterocyclic agent can also be applied to the plant as a powder, e.g. dust or moistened to form a paste, or it can be used as a coarse granulate solid by use of dry extenders such as talc, bentonite, clays, diatomaceous earth, Kaolins and other inert and conventional solid extenders in the same concentration ranges set forth for the liquid carriers.
The present compositions are applied to plants at a rate of between about 0.05 and about 100 Kg/hectare, preferably between about 0.8 and about 15 Kg/hectare of soil area, or in a weight plant dosage between about 0.001 and about 0.2 grams of N-heterocyclic agent per plant to provide the desired inhibition of ethylene generated by the plant.
Plants are treated with the present N-heterocyclic agents at any temperature normally encountered under field conditions and at any time prior to, or after harvesting, depending upon the result to be achieved.
All plants utilize and generate ethylene in the regulation of growth and development; thus, any chemical which inhibits in vivo generation of ethylene will reduce or block the effects resulting from such metabolic generation of ethylene. Specifically, the results of effective treatment with the present inhibitory agents include the following:
1. Delays the spoilage of picked fruit and vegetables and the withering of cut ornamentals.
2. Delays ripening in both growing and harvested crops.
3. Delays loosening and abscission of fruit, nuts and other crops.
4. Promotes resistance to stunting and malformation of foliage in growing crops.
5. Increases the size and weight of fruit and vegetables prior to ripening by extending the growing time.
6. Minimizes sucker formation.
7. Interrupts crop ripening after harvest during transportation to market.
8. Prevents tuber sprouting until planting.
9. Inhibits latex flow in rubber trees during inclement seasons, thereby lengthening the tree life.
10. Retards seed germination and breaking of dormancy.
11. Promotes cell and root elongation and leaf expansion.
12. Prevents underdevelopment of commercial crops and sex reversal in plants.
A substantially complete discussion of effects caused by ethylene is found in many publications, including the text, "ETHYLENE IN PLANT BIOLOGY," by Frederick B. Abeles, Academic Press, Inc., which discusses documented affects of ethylene as early as 1901 and considers particular effects on more than 60 specific varieties of plants.